The present invention relates to a semiconductor device, which can be utilized suitably to semiconductor devices using, for example, nitride semiconductors.
In recent years, semiconductor devices using group III-V compounds having a larger band gap than silicon (Si) have attracted attention. Among them, MISFETs using gallium nitride (GaN) have advantages that (1) a breakdown field is large, (2) an electron saturation velocity is high, (3) a thermal conductivity is high, (4) a good hetero-junction can be formed between AlGaN and GaN, and (5) constituent materials are non-toxic and have high safety.
For example, Japanese Unexamined Patent Application Publication No. 2008-288474 discloses an AlGaN/GaN double hetero-junction field effect transistor including a GaN buffer layer containing Fe as an impurity and an AlGaN first barrier layer. Fe in the buffer layer provides a carrier trap effect and increases the energy level in the conduction band of the buffer layer. This suppresses accumulation of carriers to the interface of the buffer layer/first barrier layer to decrease a leak current.
Further, Japanese Unexamined Patent Application Publication No. 2011-238685 discloses a HEMT having a first GaN/AlN super lattice layer in which GaN layers and AlN layers are alternately stacked in pairs and a second GaN/AlN super lattice layer in which GaN layer and AlN layer are alternately stacked in pairs so as to be in contact with the first GaN/AlN super lattice layer.